The present application relates to systems and methods for diagnosing aftertreatment component degradation in an exhaust gas aftertreatment system, and more particularly, but not exclusively, to methods and systems for diagnosing degradation of a catalysts that generate feedgas to a selective catalytic reduction (SCR) catalyst.
Control and monitoring of (SCR) catalyst performance are of increasing interest to meet modern internal combustion engine emissions standards. The efficiency of a typical SCR catalyst in removing NOx emissions is sensitive to the molar ratio of NO2 to NOx at the inlet to the SCR catalyst. Under most conditions for diesel engine operation, the ratio of NO2 to NOx at the SCR inlet is established by the operational capability of the upstream diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) since these components tend to make NO2 from NO upstream of the SCR catalyst inlet. However, as these components age, this ability to convert NO to NO2 deteriorates, and the molar ratio of NO2 to NOx at the inlet to the SCR catalyst drops. Thus, the efficiency of the SCR catalyst is reduced over time.
Diagnostic systems are typically located within a vehicle and are used to monitor operation of various systems of a vehicle. Consequently, it would be desirable to employ these diagnostic systems in monitoring the performance and/or degradation of aftertreatment components to avoid increased emissions that might occur if such events remained undetected while the vehicle continued to be operated. Accordingly, further technological developments in this area are desirable.